The present invention relates to a photo printer, and particularly to a photo printer controller having a nonvolatile memory, such as a large-capacity magnetic storage, and a volatile memory, such as a bit map memory. The invention further relates to a photo printer controller suitable for use in a computer system including an image scanner as an input device, and to the method of operation of the system.
Photo printers represented by laser beam printers, featuring low-noise, high-quality and high-speed, are now replacing conventional wire dot matrix printers and creating a new market known as desk-top publishing. A photo printer is controlled by a printer controller which converts coded print data of characters, figures and graphs sent from a host computer into print dot data which is stored in a bit map memory. The photo printer controller incorporates the bit map memory having several megabytes capacity with a magnetic storage, such as a hard disk, or floppy disk for storing character fonts and saving temporarily print data sent from the host computer, and the bit map memory has a capacity of 2 megabytes for storing a A3-size page in a print density of 300 DPI (dot per inch), or 8 megabytes for a print density of 600 DPI, as described in Japanese publication "NIKKEI ELECTRONICS", Feb. 9, 1987, pp. 144-145
Another article in "NIKKEI ELECTRONICS", Apr. 20, 1987, pp. 160-161, describes that a conventional desk-top publishing system includes a personal computer as a host computer which is directly connected with an image scanner and a photo printer with a built-in controller, and image data picked up by the image scanner is processed for enlargement, reduction, etc., by the CPU of the host computer and text areas and graphic areas are merged to complete a document page. The amount of data transferred from the image scanner to the host personal computer is as large as 1 megabyte for a A4-size page in 2-tone (black/white) printing with an image scanner having a dot density of 300 DPI.
Conventional photo printer controllers have their interface with host computers limited to one-way data ,transmission from host computer to printer, as in the CENTRONICS interface, or to low-speed bidirectional data transmission as slow as 19 kilobits/sec, as in the RS232C interface, and have their software designed to perform one-way control for solely printing data sent from the host computers. Therefore, when the printer is not working, the large-capacity magnetic storage and the bit map memory in the controller are idle (refer to U.S. Pat. No. 4 694,405).
Recently, standardization of the interface is under way for small computer's peripheral devices including hard disk units, floppy disk units, image scanners and printers, and this SCSI (Small Computer System Interface) provides a capability of 1.5 megabytes/sec, bidirectional, parallel data transmission.
In order for a small computer system to have a faster access to its hard disk or floppy disk storage, it is known that the storage needs to be provided with a memory for buffering disk transaction data. However, in the case of a conventional small computer system including a storage with associated cache memory and a photo printer, memories are separated in the host computer and photo printer, resulting in their inefficient use.
On the other hand, when a desk-top publishing system is designed to deal with a full-page data at once, a conventional host personal computer needs to have a memory of that capacity, resulting in an expensive system. In addition, the host computer has its system bus occupied by the high-speed data transfer from the image scanner, and it cannot be used for other processing during the data reading.
In an opposing case where a host personal computer is provided with only a small-capacity memory and image data from an image scanner is written into the memory in blocks, the system expends excessive time for data writing and the print quality of the written image can be degraded at the boundary of data writing blocks due to the structure of the image scanner. The combination of an image scanner and a printer controller for completing a printing system is disclosed in U.S. Pat. No. 4,706,099.
In any of the foregoing system configurations, when image data is to be edited for enlargement, rotation, etc., the data needs to be divided into small blocks for processing due to the limited memory capacity, and this will require an intricate management and troublesome operations.